Method and means for replacing an electrically conducting cable by another electrically conducting cable

ABSTRACT

Method for replacing a first cable (1) by a second cable (2) between a first predetermined point (1a) and a second predetermined point (1b). The cable comprising, 
     the provision of first series impedance means (S1) close to the first end (2a) and second series impedance means (S2) close to the second end (2b) of the second cable (2), which first (S1) and second (S2) series impedance means can be switched between a state of high impedance value and a state of low impedance value, 
     electrically connecting the second cable to the first cable (1) at the first (1a) and second (1b) points, during which operation both the first (S1) and the second (S2) series impedance means are kept in their state of high impedance value, 
     switching the first (S1) and (S2) series impedance means to their state of low impedance value before optionally removing the first cable between the first point and the second point. Wherein both the first (S1) and the second (S2) series impedance means are impedance inducing means allowing induction of an impedance within a range from a low impedance value to a high impedance value without cutting through the second cable (2).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of copending application Ser. No.08/710,953, filed Sep. 24, 1996 now U.S. Pat. No. 5,815,918.

BACKGROUND OF THE INVENTION

The present invention relates to a method for replacing a first cableprovided with at least one electrical conductor by a second cableprovided with at least one electrical conductor between a firstpredetermined point and a second predetermined point of the first cable,comprising the following steps:

a. providing the second cable with a first end there of in the vicinityof the first point, the first end being provided with a first seriesimpedance means switchable between states of high and low impedancevalue;

b. providing the second cable with a second end thereof in the vicinityof the second point, the second end being provided with a second seriesimpedance means switchable between states of high and low impedancevalue;

c. electrically connecting the at least one conductor of the secondcable at the first end to a predetermined conductor of the first cableat the first point while keeping the first impedance means in a state ofhigh impedance and electrically connecting the at least one conductor ofthe second cable at the second end to the predetermined conductor of thefirst cable at the second point while keeping the second impedance meansin a state of high impedance;

d. substantially simultaneously switching the first series impedancemeans to a state of low impedance and the second series impedance meansto a state of low impedance value;

e. cutting through the first cable between the first point and thesecond point at a location near the first point and another locationnear the second point.

Such a method is known from Electronics & Communications in Japan, partII, Electronics, part 71, Nr. 7, part 02, Jul. 1, 1988, pages 84-93,Naohisa Komatsu et al.: "Technology of cable transfer system forerror-free digital transmission".

The problem which is solved by the present invention will be explainedwith reference to FIGS. 1a to 1e. When work is carried out onoperational telecommunications cables, existing cables frequently haveto be replaced by new cables. The conventional method for this issubstantially to remove the existing cable except for a few connectingpieces and then to fit a new cable between these connecting pieces. Theproblem with this is that active telecommunications connections areinterrupted as a result. This problem has, in principle, already beensolved before by a method which is shown diagrammatically in FIGS. 1a to1e.

FIG. 1a shows a telecommunications cable 1 between two communicationpoints A and B, a section of which cable between points 1a and 1b has tobe replaced by a new cable 2. FIG. 1a shows cable 2, which has two cableends 2a, 2b, loose alongside cable 1.

FIG. 1b shows that in a first method step cable end 2a is connected topoint 1a. The cables 1, 2 are shown diagrammatically. However, it mustbe understood that the cables can each contain tens, if not hundreds, ofcores or core pairs. An engineer has to expose all of these cores andwill therefore be working for some time to connect all cores of cables 1and 2 with one another at point 1a. During this entire time cable end 2bis still not connected to cable 1.

Once the engineer has finished, he moves to point 1b and there connectscable end 2b to cable 1 following the same procedure as at point 1a.This situation is shown in FIG. 1c, from which it can be seen thatpoints 1a and 1b are connected via two parallel communication cables 1and 2.

FIG. 1d shows that the engineer then cuts through cable 1 at a pointwhich is close to point 1b and is located between points 1a and 1b, sothat only the communication link via cable 2 remains intact. He thenmoves to point 1a in order there also to cut through cable 1 at a pointbetween points 1a and 1b, as is shown in FIG. 1e. The latter figureshows that a cut-through section 1' of cable 1 remains between points 1aand 1b. Section 1' can then be removed as desired.

It will be clear that with the method illustrated in FIGS. 1a to 1e thecommunication link between points A and B is never broken.

However, with the method shown in FIGS. 1a to 1e problems occur at twopoints in time with respect to, in particular, broadband signals, whichare transmitted at high speed, for example at more than 1 MB/s, betweenpoints A and B. These points in time are shown in FIGS. 1b and 1d. Itcan be seen from FIG. 1b that cable 2 is connected by one or more coresto cable 1 at point 1a, whilst cable end 2b is still open. Especially inthe case of broadband signals which are transmitted via cores of cable 1which have already been connected to corresponding cores of cable 2,undesirable reflections then occur in the cores of cable 2. This cangive rise to dips in the transmission. In practice it is found that thiscan cause interference in modems. The consequence can even becommunication failure. These problems also arise in the situationaccording to FIG. 1d, although it is then not cable 2 which produces thereflections but the section of cable 1 between points 1a and 1b which atthat point in time has been cut through on one side only.

In practice, points 1a and 1b are often at least a few tens of metresapart. It would already be possible appreciably to shorten the durationof the undesirable situation by having two engineers workingsimultaneously at points 1a and 1b, who are able to communicate with oneanother so that they work as far as possible on the same core pairs atthe same time. By this means the undesirable situation per core pairwould be limited appreciably. However, even then some delay betweenmaking and breaking the connections at points 1a and 1b is stillunavoidable.

The prior art disclosed by Komatsu et al. referred to above discloses amethod and devices for providing series impedances at those locations ofthe cable to be replaced that need to be cut through after the lattercable is replaced by a new cable. The known method is carried out bydevices comprising switches that can be controlled remotely. A firstswitch is arranged to bypass a first location in the cable to bereplaced which first location needs to be cut through. A second switchis arranged to bypass a second location in the cable to be replacedwhich second location needs to be cut through. The devices used comprisetwo further switches and a resistor thus forming a pair transfercircuit, which is also to be connected to the ends of the new cable. Anyof the conductors of the old cable to be replaced and the new cable needto be connected to pair transfer circuits of this type. Although themethod and the device described by Komatsu et al. overcome the problemsrelated to the method illustrated with reference to FIGS. 1a to 1e, theyare still complex and there is a need for simplification.

SUMMARY OF THE INVENTION

The aim of the present invention is, therefore, to provide a method andmeans with which a first electrically conducting cable can be replacedby a second electrically conducting cable, with which an activeconnection to the first cable is not broken and connection of the secondcable results in substantially no interference to high frequencysignals, which method and means are simple compared with the prior art.

This aim is achieved by a method of the type mentioned in the preamble,characterised in that both the first and the second series impedancemeans are impedance inducing means allowing induction of an impedancewithin a range from a low impedance value to a high impedance valuewithout cutting through the second cable.

Here, "induction" is to be understood in a broad sense, i.e., inductionrefers to any act or process of causing a desired impedance value tooccur in a cable which includes electromagnetic induction. However,changing an impedance value in a piece of conductor may, theoretically,also be achieved by rising or lowering the temperature of that piece.So, inducing a desired impedance value may also be achieved bytemperature control.

It is observed that "switching" between states of high and low impedanceis intended to include changing impedance values gradually.

As a result of the use of such series impedance means, only very shortsections of the second cable will be detectable, from the electricalstandpoint, at the points in the first cable where the cores of therelevant conductors have been exposed and connected to the cores of thesecond cable, as long as the series impedance means in the second cableare kept in their state of high impedance value. Consequently,troublesome reflections no longer occur at the points while work isbeing carried out to connect conductors of the first and second cableswith one another. When the work is complete, the series impedance meansare switched to their state of low impedance value, so that the secondcable temporarily forms a parallel branch to the first cable. Thesection of the first cable between the two the points can then beremoved.

With this method, switching of the first and second series impedancemeans to their state of low impedance value prior to step c takes placesubstantially simultaneously. Simultaneous switching avoids thesituation where a substantial section of the second cable is, from theelectrical standpoint, temporarily detectable from either the first orthe second point in the first cable, which could temporarily give riseto interference.

The method according to the present invention is much simpler than themethod described in the publication of Komatsu referred to above in thatit does not to connect any additional means to either the first or thesecond cable to induce the states of high and low impedance value, whichmeans need to form a bridge across the points of the first cable to becut through and are to be disconnected afterwards.

In a further embodiment of the method according to the invention,furthermore at least prior to step e the following steps are taken:

providing third series impedance means and fourth series impedance meansin the first cable between the first point and the second point, whichthird impedance means are provided in the vicinity of the first pointand which fourth impedance means are provided in the vicinity of thesecond point, both the third and fourth series impedance means beingimpedance inducing means allowing induction of an impedance within arange from a low impedance value to a high impedance value withoutcutting through the first cable;

prior to step e both the third and the fourth series impedance means arekept in their states of low impedance value;

prior to step e, but after the first and second series impedance meanshave been switched to their states of low impedance values, both thethird and the fourth series impedance means are switched to their statesof high impedance value.

For the same reasons as to why the first and second series impedancemeans are preferably switched simultaneously, the third and fourthseries impedance means are also preferably switched to their state ofhigh impedance value substantially simultaneously prior to step e.

The invention also relates to a device for inducing a series impedancein a cable provided with at least one electrical conductor, which seriesimpedance can be varied between a state of high impedance value and astate of low impedance value and vice versa and comprises a coilarranged as a secondary winding of a transformer, the ends of which coilare connected to a switch. The method can advantageously be carried outusing a device of this type. Such a device can be used to induce eitherlow or high series impedance values in several parallel conductors in acable at the same time, just by putting the device in the vicinity ofthe conductors. This is much simpler than the device used in the priorart disclosed in the article of Komatsu e.a. referred to above, whichneeds several physical connections to any of the conductors of the firstcable to be replaced and to the conductors of the second, new cable.

The switch in the device according to the invention can be a switchwhich can be operated remotely. The remote operation can, for example,be by means of control signals transmitted via electrical or glass fibrecables or by means of control signals transmitted radiographically. Bythis means it is easily possible for two or more such series impedanceslocated a distance apart to be switched simultaneously from their oneseries impedance value to their other series impedance value.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to afew figures which are intended for illustrative purposes and not as arestriction of the invention.

FIGS. 1a to 1e illustrate a method according to the prior art forreplacing one cable having electrical conductors by another cable havingelectrical conductors;

FIGS. 2a to 2e illustrate a method according to the invention forreplacing one cable having electrical conductors by another cable havingelectrical conductors;

FIG. 3a shows a device for inducing a high series impedance in a cable;

FIG. 3b shows an equivalent electrical circuit of the device accordingto FIG. 3a.

FIG. 4 shows a receiver and a MOS switch.

In FIGS. 2a to 2e, 3a and 3b the same reference numerals are used forthe same elements as in FIGS. 1a to 1e.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 2a shows the situation where the new cable 2, to be fitted, isprovided parallel to cable 1 between the points 1a and 1b. Thedifference compared with FIG. 1a is, however, that a series impedance S1and a series impedance S2 are incorporated in cable 2. Series impedanceS1 is located close to cable end 2a, whilst series impedance S2 islocated close to cable end 2b. Each of the series impedances S1, S2 isequipped such that the series impedance can vary in impedance between ahigh and a low value. Preferably, a low impedance value approaches zeroand a high impedance value approaches ∞ within a predetermined frequencyrange. Suitable means for this will be described with reference to FIGS.3a and 3b.

The symbol "1", which indicates a state of high series impedance, isshown next to series impedances S1, S2 in FIG. 2a.

Two series impedances S3 and S4 are preferably also used between thepoints 1a and 1b in cable 1, series impedance S3 being located close topoint 1a and series impedance S4 being located close to point 1b. Therequirement in respect of series impedances S3 and S4 is that they canbe fitted to cable 1 without cable 1 having to be broken for thispurpose, so that there is no interference with transmissions takingplace. This can be effected with the aid of means which produceinductance, as will be explained below with reference to FIGS. 3a and3b.

In FIG. 2a the series impedances S3 and S4 have the symbol "0", whichindicates a low series impedance. In other words, the signals on cable 1are transmitted unattenuated by series impedances S3 and S4.

FIG. 2b shows the following step in which the relevant core pairs ofcable 2 are electrically connected at cable end 2a with the relevantexposed core pairs of cable 1. Because series impedance S1 with a highimpedance value is present close to cable end 2a, point 1a will, fromthe electrical standpoint, be connected only to a very short section ofthe total length of cable 2, namely the section between cable end 2a andseries impedance S1. As a result hardly any troublesome reflectionsoccur and there will be hardly any disturbance of the signals on cable1.

FIG. 2c shows the step in which the respective core pairs of cable end2b are connected to the respective exposed core pairs of cable 1 atpoint 1b. As series impedance S2 is also kept in the state of highimpedance during this operation, point 1b would also, from theelectrical standpoint, be connected only to a very short section ofcable 2. Therefore, at point 1b as well no troublesome reflections arisefor signals on cable 1 and there will be virtually no interference ofsignal transmission at point 1b.

It will be clear that it is possible to work at points 1a and 1b at thesame time or successively without this making any difference from theelectrical standpoint. The only condition is that both series impedanceS1 and series impedance S2 are kept in the state of high impedance.

After all desired core pairs of cables 1 and 2 have been connected toone another both at point 1a and at point 1b, both series impedance S1and series impedance S2 are switched to the state of low impedance. Ifseries impedance S1 is switched over later than series impedance S2,troublesome reflections could arise at point 1b in the interveningperiod. The same is true of point 1a if series impedance S2 is switchedover later than series impedance S1. Consequently, it is important thatswitching of series impedances S1 and S2 from the state of highimpedance to that of low impedance takes place simultaneously as far aspossible. If different engineers are working simultaneously at points 1aand 1b, this can be effected by communication between these engineers.However, it is best if the series impedances can be controlledelectrically or radiographically from one point, so that they can beswitched simultaneously by one person from the one impedance value tothe other.

At that point in time, signals can be transmitted between A and B bothvia cable 1 and via cable 2. Series impedances S3 and S4 are thenswitched to the state of high impedance, which state is shown in FIG.2d. To avoid a substantial portion of cable 1 being connected for sometime either to point 1a or to point 1b and being able to give rise tointerference via reflections, series impedances S3 and S4 are preferablyalso switched simultaneously. It is also possible for all seriesimpedances S1, S2, S3 and S4 to be switched virtually simultaneouslyprovided that series impedances S3 and S4 switch slightly later thanseries impedances S1 and S2, because the signal path via cable 1 mustnot be interrupted during the period when it has not yet beenestablished via cable 2. This switching can be effected, for example,via one electrical or radiographic instruction given by one engineer,the instruction for series impedances S3 and S4 being delayed by a fixeddelay time.

Cable 1 can then be cut through between point 1a and series impedance S3and between point 1b and series impedance S4 and the section 1' whichhas been cut free can be removed as desired. This is showndiagrammatically in FIG. 2e.

It is pointed out that series impedances S3 and S4 can optionally beomitted. To prevent troublesome reflections in the section of the cable1 between points 1a and 1b, cable 1 must then, however, be cut throughas simultaneously as possible at points 1a and 1b, after cable 2 hasbeen fitted parallel to cable 1 and series impedances S1 and S2 havebeen switched to the state of low impedance value (situationcorresponding to FIG. 2d). This procedure requires engineers workingsimultaneously at points 1a and 1b who, via the necessary communicationsequipment, synchronise cutting-through as far as possible. Since cuttingthrough is done by hand, such synchronisation can never be perfect andit will therefore be possible for interference nevertheless to arise inthe time which elapses between cutting through at point 1a and at point1b. As series impedances S3 and S4 can be switched simultaneously viaelectronic or radiographic means, the use of such means is to bepreferred.

In principle, it is conceivable that the series impedances S1 and S2consist of switches, which initially are open (state "1") and later(FIG. 2d) are closed (state "0") and are then kept definitively closed.It is conceivable to realise an embodiment of this type using existingsemiconductor techniques. However, this is expensive because theswitches can subsequently no longer easily be removed from cable 2.Furthermore, such switches can certainly not be used for seriesimpedances S3 and S4 because they would already necessitate the cuttingthrough of cable 1.

It is therefore desirable to be able to perform the method describedabove using means which can be fitted in a non-destructive manner to apredetermined point in a cable and there are able temporarily to induce,as desired, a series impedance with variable impedance value in thecable and which can be removed on completion of the method, once againin a nondestructive manner. This can be carried out according to theinvention with the device shown in FIG. 3a.

FIG. 3a shows a conductor which has been wound as a coil 4 around a core3 of suitable material and which is connected at both of its ends to aswitch 5. The core 3 consists of two semicircles which are joined to oneanother via a hinge 6. The two halves of the core 3 can be moved awayfrom and towards one another at the point opposite the hinge 6.Therefore a cable, for example the new cable 2, can be fed through thecircular core 3. The device indicated by reference numerals 2, 3, 4, 5and 6 forms one series impedance, for example S1. The hinge 6 can bereplaced by any other means for folding open or folding apart the corehalves. Although the core 3 has been shown here with two circularhalves, the halves do not have to be circular, provided they are able toform a magnetically closed circuit. The core can also consist of morethan two parts. For use with cable 2, core 3 can optionally also consistof a ferrite bead, which is pushed over cable 2 and is destroyed toobtain the state of low impedance value. To summarise, core 3 canconsist of one or more parts, which parts can assume a magneticallyclosed and a magnetically open state. Switch 5 may be replaced by anyother switching circuit able to short circuit coil 4 either by sudden orgradual switching. Switch 5 may, e.g., be replaced by a slidingresistance.

FIG. 3b shows an equivalent electrical circuit of the arrangementaccording to FIG. 3b. In this circuit cable 2 is the primary "winding"of a transformer which has core 3 and secondary winding 4. With the aidof switch 5, it is possible either to remove the power from or toshort-circuit the secondary winding. If switch 5 is closed there is aminimum impedance between the terminals of the primary "winding" and ifswitch 5 is open there is maximum impedance between the terminals ofsaid winding. By operating switch 5 it is therefore possible to induce aseries impedance which has either a high or a low impedance value at aspecific desired point in cable 2. Switch 5 can be a manually operatedswitch. However, to enable two or more series impedances to be switchedsimultaneously, it is preferable to be able to control switch 5remotely. To this end, switch 5 can, for example, be constructed as atransistor, which can be controlled remotely either via a suitablecontrol signal via an electric cable or glass fibre cable or via aradiographic signal which is converted by a suitable receiver into anelectric signal. Alternatively, a control signal of this type can alsobe transmitted acoustically or optically (through the air). A mechanicalconstruction is also possible. If the control signal is transmitted viaan electric cable, this transmission can be effected via cable 1 or 2,in which case the coil 4, which is in any case already present, can beused to apply the control signal to the cable 1, 2. A switch 5 which canbe operated radiographically is shown diagrammatically in FIG. 4. Areceiver 8 is equipped to receive a suitable control signal and toconvert the latter into an electrical control signal for the gateelectrode of MOS transistor 5', which serves as switch 5. Of course,switch 5 does not have to be a MOS transistor. The only condition isthat switch 5 can switch between a state of low impedance (notnecessarily 0 Ω) and a state of high impedance (not necessarily ∞ Ω),either by sudden or gradual switching.

As an alternative to the device shown in FIG. 3a, it is possible to usea device from which switch 5 and the conductor 4, wound as a coil, havebeen removed. In a device of this type the state in which the two halvesof the core 3 are folded together (that is to say gap 7 has been reducedto zero) then corresponds to a series impedance of maximum impedancevalue. By either folding the two halves of the core 3 away from oneanother or increasing the gap 7 from zero to a predetermined value orremoving the core as a whole, said state of maximum series impedancevalue can be switched to a state of low impedance value. However, thisnecessitates movements of mechanical parts and, although these could becontrolled remotely, they are less practical than remote control ofswitch 5.

It will be clear that the method described above is not restricted touse of one of the devices described. Any other device with which aseries impedance can be produced in a cable and the impedance of whichcan be switched between a high and a low value and vice versa is, inprinciple, suitable for this purpose.

I claim:
 1. A device for inducing a series impedance in a cable providedwith at least one electrical conductor, the device comprising:a core (3)having a construction such that it can be moved between:(i) an openstate for receiving a cable with at least one electrical conductor and(ii) a closed state far surrounding said cable, and a coil (4) woundabout said core (3) to form a secondary winding of a transformer formedby said cable, said core and said coil, said coil (4) having a first anda second end portion, respectively, connected to a first and a secondoutput terminal of a switch (5; 5'), respectively, the switch (5; 5')being switchable between a first and a second state and between thesecond state and the first state, in the first state a first impedanceand in the second state a second impedance being present between saidfirst and second terminals, said first impedance having a higherimpedance value than said second impedance, wherein said seriesimpedance in said cable can be varied between a state of a highimpedance value and a state of a low impedance value and between thestate of low impedance value and the state of high impedance value, thehigh impedance value being larger than the low impedance value, andwherein said switch (5; 5') is arranged to be remotely switchablebetween said first and second states and said second and first states bya control signal.
 2. A device according to claim 1, wherein said switchis arranged to receive said control signal via one of an electric cable,a glass fiber cable, and via a radiographic signal.
 3. A deviceaccording to claim 1, wherein said first impedance of the switch (5; 5')has a value substantially equal to 0 Ω and said second impedance of theswitch (5; 5') has a value substantially equal to ∞ Ω.
 4. A deviceaccording to claim 1, wherein said low impedance value of the cable issubstantially equal to 0 Ω and said high impedance value of the cable issubstantially equal to ∞ Ω within a predetermined frequency range.